Leukemia is a disease which belongs to hematologic malignancy, in which tumorigenic hemopoietic cells proliferate unlimitedly and appear in the blood. The disease called leukemia is mostly caused by tumorigenic leukoblasts, as well as by tumorigenic erythron and thrombocytic cells. In leukemia, there is a case that blood cells stop differentiation at a certain stage of differentiation or maturation, and undifferentiated blast cells in an upstream thereof proliferate to form tumor, while there is another case that blood cells retain an ability of differentiation or maturation despite deviation of biological regulatory ability and sign of autonomous growth. The former case corresponds to acute leukemia and the latter case to chronic leukemia or myelodysplastic syndromes (MDS). Though causes and pathogenic mechanisms are mostly unknown, it is vital to detect and treat leukemia at an early stage.
Leukemia is diagnosed e.g. by morphological observation of a blood cell, chromosomal test, or surface antigen analysis of a blood cell using flow cytometry. Meanwhile, concerning leukemia having chromosomal aberration or genetic aberration, PCR using disease-specific primer or RT-PCR is performed. It is also reported that the findings of quantitative RT-PCR of Wilms tumor gene 1 (WT-1) reflect the amount of tumor cells in leukemia (Non-Patent Document 1).
As stated above, leukemia treatment essentially requires early identification/detection, specifically that of leukemia or leukemia cells. Accordingly, this medical treatment heavily involves information of residual tumor cells (minimal residual disease (MRD)), found in e.g. the blood, particularly a bone marrow fluid, and its volume to judge therapeutic effects and determine required treatment policies.
Nevertheless, since morphological observation of a blood cell can confirm the existence of a tumor cell when its volume comes to a considerable amount, it is not appropriate for early detection of leukemia or detection of residual tumor cells. Surface antigen analysis of a blood cell using flow cytometry is expected to be effective in e.g. early detection of a tumor cell due to its favorable detection sensitivity and so on. Also, this analysis technique needs selecting a combination of cell surface antigens which are specific to a tumor cell and found on the surface thereof to be diagnosed. According to a quantitative RT-PCR of Wilms tumor gene 1 (WT-1), some cases demonstrated no expression level of the gene.
From the above observations, a method of examining leukemia in an easy and correct manner, particularly a method of examining leukemia having quantitativeness and less false positive, which is common to many kinds of leukemia, is constantly desired to be established.
Non-Patent Document 1    K. Inoue et al., Blood, 84 (9) 3071-3079 (1994)